The juveniles, ranging in age from 13 to 17, had been trafficked through social media, online classified ad services and conventional street-trolling. They are only a small part of what officials say is the much larger national problem of child prostitution.

“We are trying to take this crime out of the shadows, and put a spotlight on it,” Ron Hosko, assistant director of the FBI’s Criminal Investigative Division, said at a news conference.

The 72-hour sweep that lasted through the weekend was the seventh round of a campaign begun in 2003. State, local and federal investigators joined in the latest operation.

The FBI division in Seattle arrested nine adults and rescued three juveniles, while the FBI division in Portland rescued two juveniles and arrested 13 women and four alleged pimps, and identified a fifth.

The alleged pimps could face various trafficking and other charges. Some pimps arrested in past versions of Operation Cross Country are now serving life sentences or were sentenced to prison terms as long as 50 years.

The rescued juveniles, meanwhile, face a hard road of recovery from what officials say can be a common history of sexual, emotional and physical abuse. Nearly all of the prostitutes rescued this past weekend are female.

They are all also painfully young: One, rescued in Sacramento, is 14, the FBI said.

“This is a particularly vulnerable population,” said Drew Oosterbaan, chief of the Justice Department’s Child Exploitation and Obscenity section. “Traffickers are preying on youth with low self-esteem and minimal support.”

Many teenagers caught up in the sex trade come from broken homes, officials said. Hosko said the pimps may recruit their prey relatively gently, using compliments and rewards, but then will use violence and drugs to keep the juveniles in line.

Customers are often found at big-time sporting events, Hosko said, or they may be found through online advertising. Unlike Craigslist, the other big popular classified ad website, Backpage, still includes a listing for “escorts.”

“It is a venue that we look at very closely,” Hosko said. “We will continue to look at Backpage and other (places) where pimps gather.”

The Backpage website includes a statement denouncing “human trafficking,” and contact information for the National Center for Missing and Exploited Children. A TechCrunch article last year reported that Backpage screens for potentially troublesome keywords in submitted ads, and reports to the National Center for Missing and Exploited Children those sex ads suspected of dealing with a minor.

Since the FBI-led operation began a decade ago, more than 2,700 children have been recovered. The investigations and subsequent 1,350 convictions have resulted in lengthy sentences, including 10 life terms, and the seizure of more than $3.1 million in assets, FBI officials said.